Noobie Bike handling question

[bedfordclanger]

Hi everyone, love this website and the forums look great.

I have a real 'road bike noobie' question that may be stupid, but I would genuinely welcome any advice:

Having just bought my first road bike since I was a teenager (am now 47) I need a bit of advice.

Upon tackling a short descent I have done dozens of times on my old mtb / hybrid crossover my bike started to 'shimmy' around quite alarmingly - I stayed as calm as possible, and braked very very gently and things soon settled down.

I tackled the same descent a few days later and wasn't particuarlly worried or nervous about it happening again, but it did, and much worse in fact! This time I wasn't riding solo and my partner was quite alarmed (not half as alarmed as me!!) The bike was shimmying around like a bucking bronco and I think I was quite lucky to stay on and in one piece - once again i braked very very gingerley, being very aware that overdoing it could be very messy.

FYI the descent I am talking about is single track country lane, not smooth but not too bad, quite cambered as well, and both days conditions were fine if pretty windy, but dry road. The bike in question is an ally framed B'Twin Triban 5 from Decathlon (previous mount was a GT Transeo city/mtb crossover).

Obviously I will treat this bit of road with renewed respect but would welcome any tips or advice as to how to avoid the problem.

Thanks guys

 

[mojomonkey]

Does this sound like your situation?

 

[bedfordclanger]

Wow - that was quick Mojomokey. Thanks for that, very interesting (if very technical) reading. The fact that it seems more likely to happen on a long frame with a high saddle chimes with me, as the frame is 63cm and saddle is high - I am 6'4'' with a 35'' inside leg. Also that fatter more compliant tyres can absorb a degree of shimmy.

I recall it once happened to me about 30 years ago on old steel framed Carlton racer (though I was going much too fast) and ended up with a bent front wheel, some bruises and blood, an experience I am keen not to revisit.

Thank you once again, I will read and re-read.

 

[JayKosta]

If the wheels have a large reflector attached to the spokes, I'd remove the reflectors and see if that helps. The weight of the reflect causes the wheel to be out of balance, and if too much can cause problems.

The reflectors are good if riding in poor light conditions, but I'd use a set that are light weight if high speed riding is involved.

Jay Kosta
Endwell NY USA

 

[DirtyWorks]

Dave Moulton

Here's a plainer description from a former frame builder whom I trust.

A bike with a shimmy problem usually has a design flaw in the frame and there is little you can do to correct it short of changing the frame. However do check that the head bearings are not loose. Also fitting a slightly heavier tire to the front wheel may increase the gyroscopic action.

http://davesbikeblog.squarespace.com/blog/2005/11/12/high-speed-shimmy.html

And yes, bikes sold worldwide with fundamental design flaws are more common than is frequently understood.

 

[StyrbjornSterki]

A too-loose headset can cause shimmy. Or a front wheel that doesn't have enough tension on its quick release. Or a frame that's too "noodly" for your body weight. In the past, under-engineered aluminium frames (like the Vitus 992) have shown more susceptibility to the problem.

If it happens again, you can calm the frame a bit by "midshipping" your pedals (crank arms horizontal, feet same distance off the ground) and clamping the top tube between your knees. Squeeze hard. Bracing the toptube with your thighs serves to dampen the resonance that allows the shimmy to set up.

 

[Master50]

Can't add much to what is said about dealing with the shimmy. There is a new theory of bifurcation that explains the reason for a shimmy. Leonard Zinn linked the article in his velonews editorials. I owned a vitus and have not enjoyed the resonance, no! bifurcation problem I took a ferry to avoid another decent of the hill I would have crossed to get home the experience scared me so much. Amazing how increasingly flexible that bike got. Very comfortable as the flex got worse.
One point not mentioned is weight distribution. I was wondering if you came from an upright position if you are trying to keep your head up and weight to the back of the bike? you do need to balance your weight front to back as well.
Oh and if you want advice for tall riders the Zinn articles often touch on your special dimensions as he is a specialist for tall riders too.

 

[bedfordclanger]

If the wheels have a large reflector attached to the spokes, I'd remove the reflectors and see if that helps. The weight of the reflect causes the wheel to be out of balance, and if too much can cause problems.

The reflectors are good if riding in poor light conditions, but I'd use a set that are light weight if high speed riding is involved.

Jay Kosta
Endwell NY USA

Hi Jay, have removed the reflectors - every little helps - thanks for your input.

 

[bedfordclanger]

Thanks for the replies guys. I was surprised to realise that shimmy / death wobble is quite a widespread phenomenon with plenty of info on the subject on the 'net. I had assumed it was poor riding position or handling by myself. I am sure that that IS a factor, but the fact that the shimmy happened twice on the same descent, (not the fastest on that circuit, but with the worst road surface and camber changes), cannot be a coincidence.

I am sure as a newbie in term of riding a drop bar bike my handling skills have a lot to be desired, but it would seem that my knowledge of the previous rides shimmy undoubtedly led me to grip the bars firmer on the second ride, which I now know is the WRONG thing to do.

I read of one guy in California who experienced the shimmy on both his Trek, and his Felt, and having tried various wheel / tire combos, gave up on the Felt as he decided the handling was a bit too twitchy, exaggerating the problem. I think that is what I am experiencing - the directness of a road bike is still new to me after years of mtb / hybrid crossover / flat bar bikes.

Thanks again for all the replies and I look forward to reading and learning more from this excellent and unusually freindly forum.

 

[DirtyWorks]

I read of one guy in California who experienced the shimmy on both his Trek, and his Felt, and having tried various wheel / tire combos, gave up on the Felt as he decided the handling was a bit too twitchy, exaggerating the problem. I think that is what I am experiencing - the directness of a road bike is still new to me after years of mtb / hybrid crossover / flat bar bikes.

Both companies have ordered and sold poorly designed bikes in the past.

 

[Nederick]

What sort of fork do you have on the bike?
I bought a (second hand) Pinarello Paris a few years back. It had been a while since my racing days. Anyway, I found the bike very twitchy. Not particularly enjoyable handling. After ditching the forks (the wavy fork on it) for a more traditional fork (Easton 90), well my mechanic did (thanks Dad), problem solved. It was a bit fiddly in this instance with the bearing dimensions. Not only did I find the flattish bladed Pinarello fork bad at catching gusty side wind (I ride past a lot of hedgerows where gaps can let a good gust of sidewind hit you), but the more vertical end of the fork that points down to the road rather than with forward rake, I think was my problem.

More here;
http://davesbikeblog.squarespace.com/blog/2005/11/12/high-speed-shimmy.html

 

[badboyberty]

I'd suspect "the grip of death" may explain at least part of your experiences. My suspicion (based on no evidence ) is that you are holding your bars tightly and locking your elbows and shoulders. This stops the bike "auto-correcting" itself and your subsequent attempts to keep it straight will result in a positive feedback loop. It's easier said than done, but try to get as much tension out of your arms and hands as possible and let the bars move a little in your hands. Thanks to procession and the gyroscopic effect your bike wants to stay upright and moving forward. The important thing is to be conscious of your body weight on the bike. Get yourself low and back with your knees and elbows slightly bent so your centre of gravity can move with the terrain, with your eyes tracking as far ahead as possible to guide you through the corners.

Watch the MTB World Cup Downhill this weekend on Redbull TV to see how well a relaxed rider can bounce through the world's sketchiest terrain. If you ever get coaching or ride with any of those types of guys you quickly pick up that 99% of descending is bent elbows and lifted chins.

 

[winkybiker]

Both companies have ordered and sold poorly designed bikes in the past.

I had two Trek OCLV 5000 series bikes and although I didn't realise it at the time, they both handled appallingly. Twitchy and nervous but without being obediently responsive is how I'd put it. All downside. Scary to ride no-handed. But no high-speed shimmy.

Not until moving to a BMC Pro Machine did I experience a nice handling frame (and even that isn't at the very top end - perhaps a little too flexy for ultimate precision at speed). No shimmy, though.

My Colnago C59 handles flawlessly .

 

[42x16ss]

My Colnago C59 handles flawlessly .

As you'd expect

One thing that I haven't seen brought up, is your bike fit. Have you been to a decent fitter to get your position checked? Where your bodyweight is placed on the bike can have almost as much effect on handling as it does on power generation and it is also the best way to check that you are using the correct size bar and stem. Too short a stem can give twitchy handling, while too long a stem can make the bike feel very slow to handle.

 

[winkybiker]

One thing that I haven't seen brought up, is your bike fit. Have you been to a decent fitter to get your position checked? Where your bodyweight is placed on the bike can have almost as much effect on handling as it does on power generation and it is also the best way to check that you are using the correct size bar and stem. Too short a stem can give twitchy handling, while too long a stem can make the bike feel very slow to handle.

I'd second this. Getting the right weight distribution can be critical to stable handling. Seat setback, stem length and handlebar height all interact to fine tune this. But if you're on a very wrong-sized frame, you'll struggle to get it all working OK.

 

[bedfordclanger]

Thanks or all the input guys

I'd suspect "the grip of death" may explain at least part of your experiences. My suspicion (based on no evidence ) is that you are holding your bars tightly and locking your elbows and shoulders.

Think this hits the nail on the head. As previously stated I went into the descent knowing that i had the shimmy a couple of days previously, so undoubtedly was gripping the bars harder and not so relaxed which is all wrong.

The biggest revelation to me, as a slightly overweight returner to road bikes (after a 30 year absence), is not how much faster a light bike allows me to climb, sure it helps, but.... the real difference in changing from my last bike, a GT Transeo citycross bike (I kept the front suspension locked out all the time - within months of buying the bike I went from trail riding to 30 - 50 mile road rides - I never realised how much I would enjoy it!) No, the real difference is the rate at which I now pick up speed on the descents, and the average speed I can maintain on the flat, all due to massively decreased rolling resistance and enhanced aerodynamics. The GT came with Schwalbe Landcruise tyres 700 / 40, which I got about 2500 miles out of, then changing to a cheap 700 / 35 tyre as I had by now bought my new B'Twin road bike, so the GT is now a shopping / riding with the kids hack bike (all it was ever really good for in the first place really). My new ride runs Hutchinson Equinox 700 / 23, (I think in my youth the bike I had then probably had 25 or 28 but def not 23's), and the rate at which which I now pick up speed in descents is a joy to behold. But armed with my tips on what to do should shimmy strike (and it has only happened, admittedly twice, on one particular descent. On longer straighter, smoother and or faster descents all has been fine), and the knowledge not to hold the bars in a death grip, and to relax a bit more, hopefully all will be well.

 

[Hawkwood]

Fork Rake and Trail

This doesn't sound like something you're doing wrong, it sounds more like a frame issue, unless there is an obvious issue with the headset, or the forks are out of alignment. I have had exactly this issue with a hand built British frame I bought back in the 1990s, at about 30 mph and up it would start to shimmy. Nothing I tried could prevent this, and it certainly was not down to gripping the bars too tightly. I'm not an expert but from what I've read a bike's steering relies on trail which is a combination of head angle and fork rake. Get the trail wrong and there is nothing you can do to prevent a shimmy. Another poster has mentioned changing the forks, this may well work if the rake is different, as it will change the trail. Good bike manufacturers will know what head tube angles, and fork rakes will work, it's not rocket science. In your case I think you should take the bike back and asked for it to be checked. In my case I got rid of the frame, and bought a Bianchi and it was immediately back to enjoying shimmyless descending at 50 mph+.